Dynamic braking is herein understood as the braking of a rotary element when produced in direct response to the rotational input to this element. This type of braking is most commonly used in fire escape pulley devices to limit the speed of rotation of the pulley and, thus, of descent of a person hanging on the cable of such devices.
The known fire escape devices produce dynamic braking by camming action of a rotor on movable bodies freely mounted between the rotor and braking segments. Consequently, the rotational speed of the rotor increases in direct proportion to the weight of a user hanging on the cable of such devices. This is clearly not satisfactory.
In our previous patents (U.S. Pat. No. 4,198,033 of Apr. 15, 1980 and Canadian Pat. No. 1,062,180 of Sept. 11, 1979), we have proposed a dynamically braked machine wherein the rotational speed limit increases as a function of the square root of the increase of a user's weight. The present invention disclosed herein uses a similar principle of torque limitation means and is an improved variation of our previous patents.